Grails 3.2 log implicit property is assumed to be commons logging instead of slf4j

The Grails plugin seems to assume the implicit log property added to all Grails 3.2.x artefacts are Commons Logging objects, however, in Grails 3.2.x the log objects were [changed to slf4j](http://docs.grails.org/latest/guide/upgrading.html#_slf4j_now_default). This means that using a log method like `log.debug('Test {}', 'test')` compiles and runs without error but gets marked as an error in the IDE and autocompletion options are all from commons logging.

Steps to reproduce:
1. `sdk use grails 3.2.11`
2. `grails create-app test`
3. Create any grails artefact, eg a controller
4. Import test project into IDE
5. Attempt to use autocomplete on implicit log property in artefact

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*Imported from [IDEA-176469](https://youtrack.jetbrains.com/issue/IDEA-176469) · Type: Bug · Votes: 8*
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Reproduce the problem with Grails 3.2.11 by creating an application and artefact, then importing it into IntelliJ IDEA. Start by tracing how the plugin types the implicit log property and compare that with Grails 3.2.x's SLF4J default; it is done when SLF4J methods and autocomplete are recognized without an IDE error.

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